CN103633188A - Method for forming solar battery doped region - Google Patents

Abstract

The invention relates to a method for forming a solar battery doped region. The method comprises the following steps that (1) a passivation layer is formed on the surface of a semiconductor substrate; (2) an ion injection method is adopted, and an impurity source region is formed on the semiconductor substrate in a way of penetrating through the passivation layer; (3) laser is adopted for irradiating the impurity source region so that the impurity source region is activated to obtain the solar battery doped region. The method has the advantages that the laser is adopted for activating the doped region, the speed and power regulation of the laser is convenient and fast, and the response speed is high, so the precise control on the doping concentration, the doping depth and the doping width can be realized, and the process conditions are simplified.

Description

Method for forming doped region of solar cell

technical field

The invention relates to a method for forming a doped region of a solar cell, in particular to a method for forming a doped region or a selectively doped region of a solar cell by laser activating an ion-implanted impurity source, the method comprising forming an N-type doped region on a solar cell Doping (n++) regions or forming P-type doping (p++) regions belongs to the field of photovoltaic doping technology.

Background technique

Due to the limited supply of conventional energy and the increase in environmental protection pressure, many countries in the world have set off an upsurge in the development and utilization of solar energy and renewable energy, and solar energy utilization technology has developed rapidly. The application of electric energy is more and more extensive. The solar cell is one of the most common devices used to convert solar energy into electrical energy. In practical applications, the basic application unit is generally a battery module composed of multiple solar cells connected in series (welded and connected in series with interconnecting bars).

Doping is the basic process in the preparation of solar cells, which refers to artificially doping the required impurities into the thin layer on the surface of the silicon wafer in a certain way (thermal diffusion, ion implantation), and making it reach the specified amount and meet the requirements. The requested distribution form. Doping can not only make pn junctions, but also make resistors, ohmic contacts, interconnect lines, etc. Among them, ion implantation refers to ionizing impurities into ions and focusing them into ion beams, which are accelerated in an electric field to obtain extremely high kinetic energy, and then implanted into silicon wafers (called "targets") to achieve doping.

Most of the impurity sources ion-implanted into the silicon wafer stay at the gap position of the silicon atoms, and the impurity atoms at this position will not release carriers, and will not change the electrical characteristics of the semiconductor. Thus the purpose of doping cannot be achieved. After ion implantation and doping, proper annealing treatment (also known as activation, annealing) must be performed, so that the implanted impurity atoms bond with the silicon atoms in the crystal lattice to release carriers, thereby changing the electrical characteristics of the conductor. Known as electrical activation of impurity atoms, annealing can also reduce implant damage. A proper annealing process can activate the implanted impurities and minimize secondary defects.

At present, in the field of solar cells, the emitter formed by ion implantation of dopants is mainly formed by high temperature activation, while the selective emitter formed by ion implantation needs to increase the implantation dose in the heavily doped region, and then be formed by high temperature activation. The temperature required for the process is generally around 900-1100°C, and is generally carried out by rapid thermal processing (Rapid Thermal Processing, RTP) and a tubular annealing furnace. Although it can meet the doping requirements, the required activation process temperature is too high, and the process is relatively complicated, especially the high-temperature activation process will greatly reduce the bulk minority carrier lifetime of the silicon wafer, so the process adaptability is relatively poor, and it is not suitable for silicon wafers. Poor quality silicon wafers, especially polycrystalline silicon wafers which are currently in greatest demand. In addition, the high-temperature process is a high-energy-consuming process, and the activation cost is high, and the high-temperature activation process can only be carried out in the front-end process of the battery process, not in the back-end process, and the process flexibility is small.

Contents of the invention

The invention provides a method for forming a doped region of a solar cell, aiming to solve the problems of high-temperature activation on silicon wafer quality, complex process and high activation cost.

In order to achieve the above object, the first technical solution adopted in the present invention is: a method for forming a doped region of a solar cell, comprising the following steps:

(1) Forming a passivation layer on the surface of a semiconductor substrate;

(2) Forming an impurity source region on the semiconductor substrate through the passivation layer by ion implantation;

(3) Using laser light to irradiate the impurity source region to activate it to obtain the doped region of the solar cell.

In a preferred embodiment, the thickness of the passivation layer is 10nm-500nm. The preferred range is from 60nm to 300nm.

In a preferred embodiment, the generator of the laser is a pulse laser or a continuous wave laser; the wavelength range of the laser is from the ultraviolet band to the infrared band; the power of the laser is 2W-1OW; The speed is lmm/s-6000mm/s.

In a preferred embodiment, the passivation layer is also an anti-reflection layer.

In a preferred embodiment, the passivation layer is a silicon nitride passivation layer, a silicon dioxide passivation layer or an aluminum oxide passivation layer.

In order to achieve the above object, the second technical solution adopted in the present invention is: a method for forming a doped region of a solar cell, comprising the following steps:

(1) Forming an impurity source region on a semiconductor substrate by ion implantation;

(2) forming a passivation layer on the surface of the side of the semiconductor substrate having the impurity source region;

(3) Using laser light to irradiate the impurity source region to activate it to obtain the doped region of the solar cell.

In a preferred embodiment, the thickness of the passivation layer is 10nm-500nm. The preferred range is from 60nm to 300nm.

In a preferred embodiment, the generator of the laser is a pulse laser or a continuous wave laser; the wavelength range of the laser is from the ultraviolet band to the infrared band; the power of the laser is 2W-1OW; The speed is lmm/s-6000mm/s.

In a preferred embodiment, the passivation layer is also an anti-reflection layer.

In a preferred embodiment, the passivation layer is a silicon nitride passivation layer, a silicon dioxide passivation layer or an aluminum oxide passivation layer.

The relevant content in the above-mentioned technical scheme is explained as follows:

1. In the above scheme, the passivation layer is formed on the entire surface of the semiconductor substrate (silicon wafer). However, the impurity source region can be formed on the entire surface of the semiconductor substrate (silicon wafer) (for example, in the step of manufacturing a uniform junction solar cell, it is necessary to form a doped region on the entire surface of one side of the semiconductor substrate) or locally Surface (for example, when making a selective emitter solar cell, the surface of the semiconductor substrate refers to the heavily doped deep diffusion region formed under the electrode grid line and its vicinity).

2. In the above solution, the semiconductor substrate can be an N-type monocrystalline silicon wafer, an N-type polycrystalline silicon wafer, a P-type monocrystalline silicon wafer or a P-type polycrystalline silicon wafer.

3. In the above scheme, the laser generator can adopt common lasers such as: hydrofluorine laser (ultraviolet light, wavelength 193 nanometers), atmosphere fluorine laser (ultraviolet light, wavelength 248 nanometers), ammonium chlorine laser (ultraviolet light, wavelength 308nm), nitrogen laser (ultraviolet light, wavelength 337nm), hydrogen laser (blue light, wavelength 488nm), hydrogen laser (green light, wavelength 514nm), helium-neon laser (green light, wavelength 543nm), helium-neon laser Laser (red light, wavelength 633 nanometers), rhodamine 6G dye (adjustable light, wavelength 57.-650 nanometers), ruby (CrA103) red light, wavelength 694 nanometers), Qianyi aluminum garnet (near infrared light, wavelength 1064 nanometers) and carbon dioxide (far-infrared light, wavelength 10600 nanometers). The wavelength range can be selected from 20 nm to 10600 nm.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages and effects compared with the prior art:

1. The present invention uses a laser to activate the doped region. Since the speed and power of the laser can be adjusted conveniently and quickly, and the response speed is fast, precise control of the doping concentration, doping depth, and width of the doping region can be realized, making the process conditions simplify.

2. The present invention can be carried out at room temperature, and the required temperature is low, so that it can adapt to poor-quality monocrystalline silicon wafers and ordinary polycrystalline silicon wafers.

Description of drawings

Accompanying drawing 1 is the schematic diagram of the p-type silicon chip after ion implantation of pentavalent elements;

Accompanying drawing 2 is a schematic diagram of using laser to irradiate specific parts of the ion implantation area after the p-type silicon wafer is ion-implanted with pentavalent elements;

Attached Figure 3 is a schematic diagram of regional n++ formed after ion-implantation of pentavalent elements on p-type silicon wafers, using laser to irradiate specific parts of the ion-implantation area;

Attached Figure 4 is a schematic diagram of the p-type silicon wafer after ion implantation of trivalent elements;

Accompanying drawing 5 is a schematic diagram of using laser to irradiate specific parts of the ion implantation area after the p-type silicon wafer is ion-implanted with trivalent elements;

Accompanying drawing 6 is a schematic diagram of regional p++ formed after ion-implanting trivalent elements on p-type silicon wafers, using laser to irradiate specific parts of the ion-implantation area;

Figure 7 is a schematic diagram of the formation of regional n++ and p++ on the two surfaces of a p-type silicon wafer by ion implantation and laser activation processes.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

Embodiment one: the method for forming solar cell doped region

See accompanying drawing 1, accompanying drawing 2 and shown in accompanying drawing 3, a kind of method for forming solar cell doped region, prepare selective emitter solar cell with this method, concrete operation steps are:

①. Select a P-type monocrystalline silicon wafer 1 with a resistivity of 0. 5-3 } "cm, and in a mixed solution of NaOH and isopropanol, at a temperature of 90°C, perform texture etching on the surface of the silicon wafer. After obtaining suede with uniform size, soak in dilute hydrochloric acid and hydrofluoric acid solution for 5 minutes, and finally rinse with deionized water and spin dry.

②. Using a conventional diffusion furnace (conventional thermal diffusion process), phosphorous oxychloride (POC13) is used to diffuse phosphorus on the surface of silicon wafers. During diffusion, the silicon wafers are placed back to back on a quartz boat. The constant temperature zone of the diffusion furnace is 800-10000C. The time is 10-50 minutes, and a layer of n-type emitter junction 2 is formed on the surface of the silicon wafer after diffusion.

③. After diffusion, a layer of phosphosilicate glass (silicon dioxide containing phosphorus pentoxide) will be formed on the surface of the silicon wafer. Due to its poor stability and optical matching, it will affect the performance of the battery and must be removed. Acids can dissolve silicon dioxide because hydrofluoric acid reacts with silicon dioxide to form volatile silicon tetrafluoride gas. In addition, there is a thin layer of pn junction around the diffused silicon wafer, which makes the front and back of the silicon wafer directly conduct and cause leakage. Wet etching machine is used to use the mixed solution of hydrofluoric acid and nitric acid to clean the pn junction around the silicon wafer. Junction corrodes.

④. Ion implantation of phosphorus (P) dopant in the local area of the n-type emitter junction surface of the silicon wafer. The dopant can also be arsenic (As), antimony (Sb) or bismuth (Bi) of the same family as phosphorus. This step is to form an impurity source region in a local area on a semiconductor substrate (silicon wafer) by means of ion implantation. The injection dose is lEl5cm2-lEl6cm2, and the injection depth is 0. gum-1 Oum.

⑤. A layer of silicon nitride is formed as a passivation layer 3 by PECVD on the surface of the silicon wafer after ion implantation, and its thickness is 60-70 nanometers, which is also the anti-reflection layer of the solar cell. As shown in accompanying drawing 1, this step is to form a passivation layer (passivation layer is formed on the whole surface of silicon wafer) on the side surface that has described impurity source region on described semiconductor substrate (silicon wafer, rather than limited to the impurity source region).

6. In order to obtain the desired device characteristics, the laser irradiation conditions are selected as required according to the diffusion depth and activation ratio of the dopant. The specific conditions of this embodiment are: the laser 4-beam source uses Q-switched Nd:YVO and lasers, which pass through Double the frequency and the emission has a wavelength of λ = 532nm. The pulse frequency is in the range of 10kHz to 100KHz, and the optimum pulse energy density is in the range of 2 to 6J/cm 2 . The laser beam is directed through a cylindrical lens to produce a linear focus, which has a focal length of f = 200mm. The laser beam was imaged on the silicon wafer through an objective lens with a focal length of f = 50 mm. Laser is used to activate the area under the grid lines on the front of the solar cell, as shown in Figure 2, after laser irradiation, grooves will be made on the surface of silicon nitride, and n++ heavily doped regions 5 will be formed in the grooved areas, as shown in Figure 2. As shown in Figure 3, the doping concentration and depth of this region can be adjusted by changing the emission energy of the laser. This heavily doped region serves as the selective emitter of the solar cell and is well formed with the metallization process that will be mentioned later. ohmic contact. This step is laser activation of the impurity source region to obtain a selectively deep diffused heavily doped region. The power of the laser is 7W; the speed of the laser is 2500mm/s.

⑦. Form a silver electrode and a layer of aluminum film on the back of the silicon wafer by screen printing, and then dry it.

⑧. Use screen printing to print a layer of silver paste on the n++ heavily doped region 5 formed by laser activation, and then dry it.

⑨. Place the silicon wafer in a sintering furnace and heat it to the required temperature in a nitrogen atmosphere for rapid sintering. After sintering, an aluminum back field is formed on the back side of the silicon wafer, and the silver on the front side of the silicon wafer forms a good ohmic contact with the n++ heavily doped region 5, and the emitter without the formation of the n++ heavily doped region 5 can be low in diffusion concentration and diffused. The structure with small depth can effectively improve the blue light response. The battery is now complete and ready for testing.

The solar cell prepared by this method is a selective emitter solar cell. Of course, the technology of the present invention can also be used to manufacture a uniform junction solar cell and a partial contact cell on the back, thereby effectively improving the electrical performance of the solar cell.

Aiming at the disadvantages of high process temperature and complex process conditions in the prior art (high temperature activation), the present invention uses laser to activate the doped region, the process is carried out at room temperature, and the required process temperature is low, which is completely suitable for single cells with poor quality. Crystalline silicon wafers and ordinary polycrystalline silicon wafers. In addition, the activation process is simple, and the process control is precise. Combined with the control of ion implantation and laser parameters, precise control of doping concentration, doping depth, and doping region width can be realized. The important thing is that this method can easily achieve selective activation on the surface of the silicon wafer. In the high-concentration doped area where metal contact is required, heavy doping can be performed by controlling the laser parameters to reduce the contact resistance, thereby reducing the series resistance of the solar cell. Improve the fill factor of solar cells. More importantly, this process can also perfectly match the back passivation structure to form a local high-concentration doped region on the back to make a back partial contact cell.

Described passivation layer also can be the technical scheme of following example: 1, the lamination structure that aluminum oxide (A1203) layer and silicon nitride (SiNX) layer are formed; 2, silicon dioxide (SiO 2 ) layer and silicon nitride (SiNX) layer ) layer structure.

The effect of the passivation layer: (1) anti-reflection effect, which can reduce the reflection of laser light during laser activation and increase the laser energy on the surface of the silicon wafer. (2) The buffering effect can reduce the damage caused by the laser to the surface of the silicon wafer and improve the quality of the activated silicon wafer. (This is more important for the activation process. From the surface, the groove after activation is relatively narrow. If there is no such film (passivation layer), the damage to the silicon wafer is relatively large, and the groove is relatively wide. The role of silicon oxide in this respect It is better than silicon nitride, but the refractive index of silicon oxide is relatively low, so it is not suitable for anti-reflection layer, and another point is that silicon oxide is a high-temperature process). (3) Passivation, such as using silicon nitride, PECVD deposited silicon nitride can effectively passivate the surface of the silicon wafer and the silicon body, improve the minority carrier lifetime, and increase the photoelectric conversion efficiency of the solar cell. When the passivation layer is first formed and then the dopant is ion-implanted, the damage to the surface of the silicon wafer by the ion-implantation can also be reduced.

Embodiment 2, the method for forming the doped region of the solar cell

See accompanying drawing 4, accompanying drawing 5 and accompanying drawing 6, a kind of method for forming solar cell doped region, the back contact structure of solar cell prepared by this method, specific operation steps are:

①. Follow steps ①, ②, and ③ in Example 1 to prepare silicon wafers.

②. As shown in Figure 4, a layer of silicon dioxide is formed on the back surface of the P-type single crystal silicon wafer 1 as a passivation layer 3. This step is to form a passivation layer on the surface (whole surface) of a semiconductor substrate (silicon wafer).

③. Perform ion implantation of boron (B) dopant on the back surface of the silicon wafer. The dopant can also be aluminum (A1), gallium (Ga) and indium (n) of the same family as boron. This step is to use ion implantation to pass through the passivation layer (silicon dioxide passivation layer) to form an impurity source region on the semiconductor substrate.

④. In order to obtain the desired device characteristics, the laser irradiation conditions should be selected according to the diffusion depth and activation ratio of the dopant. Use laser 4 to activate the irradiation of the back area of the solar cell. The pattern of the irradiation area can be a point or a line. As shown in Figure 5, after the laser irradiation, the silicon dioxide surface will be grooved, and the The p++ heavily doped region 6 is formed in the region, as shown in Figure 6, the doping concentration and depth of this region can be adjusted by changing the emission energy of the laser, and this heavily doped region can be used as a local contact point or The local contact line forms a good ohmic contact with the metallization process mentioned later.

⑤. Form a layer of aluminum film and silver electrode on the back surface of the silicon wafer by screen printing, thermal evaporation or sputtering, and dry it.

⑥. Use screen printing to print silver paste with a certain grid line structure on the front surface of the silicon wafer, and dry it.

⑦. Place the silicon wafer in a sintering furnace and heat it to the required temperature in a nitrogen atmosphere for rapid sintering. After sintering, the silver on the front side of the silicon wafer forms an ohmic contact with the diffusion region, the aluminum on the backside of the silicon wafer forms a good ohmic contact with the p++ heavily doped region 6 formed after laser activation, and the place where the p++ region is not formed is covered with nitrogen Si is passivated, which effectively reduces the surface recombination. The battery is now complete and ready for testing.

The power of the laser used is 5W; the speed of the laser is 500mm/s.

Embodiment 3, the method for forming the doped region of the solar cell

The selective emitter (the method is the same as in Example 1) and the backside partial contact (the method is the same as in Example 2) are prepared simultaneously by laser activation.

On the basis of the above two embodiments, a solar cell with both a front selective emitter and a rear partial contact structure can be formed on a silicon wafer. The schematic diagram of the structure is shown in Figure 7.

The power of the laser used is 3W; the speed of the laser is 5000mm/s.

Embodiment 4. The method for forming the doped region of the solar cell

 Ion implantation and laser activation are used instead of high-temperature diffusion of phosphorus (or boron) to form a pn junction.

On the surface of the p (n) silicon wafer, ion implantation of phosphorus source (or boron source) is used, and then a passivation layer is deposited, and then the surface of the silicon wafer is activated by laser scanning to form a pn junction. For p-type cells, this method can be used to replace the aluminum back field formed by screen printing or the B back field formed by high temperature boron expansion process. For n-type solar cells, this method can be used to quickly form a better B-emitter junction, replacing the B-emitter junction formed by the conventional high-temperature boron expansion process or the Al back junction formed by screen printing, and solar cells can be fabricated on this basis.

The power of the laser used is 9W; the speed of the laser is 80mm/s.

The above-mentioned embodiments are only to illustrate the technical conception and characteristics of the present invention. The purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (10)

1. A method for forming a doped region of a solar cell, characterized in that: comprises the following steps: (1) Forming a passivation layer on the surface of a semiconductor substrate; (2) Forming an impurity source region on the semiconductor substrate through the passivation layer by means of ion implantation; (3) Using laser light to irradiate the impurity source region to activate it to obtain the doped region of the solar cell. 2. The method for forming a solar cell doped region according to claim 1, characterized in that: the thickness of the passivation layer is 10nm-500nm. 3. The method for forming a solar cell doped region according to claim 1, characterized in that: the generator of the laser is a pulse laser or a continuous wave laser; the wavelength range of the laser is from the ultraviolet band to the infrared band; The power of the laser is 2W-1OW; the speed of the laser is 1mm/s-6000mm/s. 4. The method for forming a solar cell doped region according to claim 1, characterized in that: the passivation layer is also an anti-reflection layer. 5. The method for forming a doped region of a solar cell according to claim 1, wherein the passivation layer is a silicon nitride passivation layer, a silicon dioxide passivation layer or an aluminum oxide passivation layer. 6. A method for forming a doped region of a solar cell, characterized in that: comprising the following steps: (1) Forming impurity source regions on a semiconductor substrate by means of ion implantation; (2) forming a passivation layer on the surface of the side of the semiconductor substrate having the impurity source region; (3) Using laser light to irradiate the impurity source region to activate it to obtain the doped region of the solar cell. 7. The method for forming a solar cell doped region according to claim 6, characterized in that: the thickness of the passivation layer is 10nm-500nm. 8. The method for forming a doped region of a solar cell according to claim 6, characterized in that: the generator of the laser is a pulse laser or a continuous wave laser; the wavelength range of the laser is from the ultraviolet band to the infrared band; The power of the laser is 2W-1OW; the speed of the laser is 1mm/s-6000mm/s. 9. The method for forming a doped region of a solar cell according to claim 6, characterized in that: the passivation layer is also an anti-reflection layer. 10. The method for forming a doped region of a solar cell according to claim 6, wherein the passivation layer is a silicon nitride passivation layer, a silicon dioxide passivation layer or an aluminum oxide passivation layer.

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